1. Field of the Invention
The present invention relates to a non-reciprocal circuit element used for a mobile communication unit including an automobile telephone or a portable telephone mainly used in a microwave band, particularly to an isolator and a circulator. Moreover, the present invention relates to a board on which non-reciprocal circuit elements are mounted.
2. Related Art of the Invention
Because a LUMPED ELEMENT TYPE isolator can be compactly configured as a non-reciprocal element circuit used for a terminal of a mobile communication unit, it has been early used and further compacted and decreased in loss.
Conventionally, an isolator has been set between a power amplifier and an antenna at a transmission stage in order to prevent an unnecessary signal from being returned to the power amplifier and stabilize the impedance at the load side of the power amplifier. Characteristics required for an isolator include a large backward loss required for the above functions and a small forward loss for reducing the power consumption at a transmission stage and lengthening the service life of a battery. Therefore, the improvement of characteristics of an isolator has been concentrated on how to improve the above characteristics in a frequency band used.
Because terminal units have been suddenly downsized recently, it is attempted not only to downsize the parts used but also to reduce the number of parts by using a multifunctional part. In case of an isolator, it is attempted to downsize the single product and moreover, it is attempted to secure the attenuation at a frequency higher than the frequency band used for the isolator and omit an LPF (Low Pass Filter) used for a transmission stage by adding functions of the LPF to the isolator.
However, because it has been difficult so far to add functions of an LPF to an isolator without deteriorating the characteristic of a frequency band used for the isolator, there has been a problem on practical use.
It is an object of the first aspect of the present invention to provide an isolator added with LPF functions without deteriorating the characteristic of a conventional frequency band used for the isolator in order to solve the above conventional problems.
The general configuration of a LUMPED ELEMENT TYPE isolator widely used for terminals of portable telephones at present will be briefly described below by referring to FIG. 31. Three sets of strip lines 61Aa, 61Ab, 61Ac electrically insulated, crossed at an angle of 120xc2x0, and overlapped each other are arranged on a ferrite disk 62A, and a magnet 63A for magnetizing the ferrite disk 62A is set so as to face the ferrite disk 62A. One ends of the strip lines 61Aa and 61Ab are connected with input/output terminals 65Aa and 65Ab and one end of the strip line 61Ac is terminated by a predetermined resistance 66A.
Moreover, capacitors 64Aa, 64Ab, and 64Ac are added to one ends of the strip lines 61Aa, 61Ab, and 61Ac in parallel with the input/output terminals 65Aa and 65Ab or the resistance 66A. Moreover, the other ends of the strip lines 61Aa, 61Ab, and 61Ac are respectively grounded. Then, an upper case 67A and a lower case 68A are set which serve as a part of a magnetic circuit and contain the ferrite disk 62A, the magnet 63A and the strip lines 61Aa, 61Ab, and 61Ac. 
It is described below that the upper case 67A and the lower case 68A serve as a part of the magnetic circuit. If neither upper case 67A nor lower case 68A are used, the magnetic flux emitted from one side of the magnet 63A returns to the other side of the magnet 63A after passing through an infinite route. However, when forming the upper case 67A and the lower case 68A with, for example, a magnetic material such as iron and covering the magnet 63A with the upper case 67A and the lower case 68A, the magnetic flux emitted from one side of the magnet 63A returns to the other side of the magnet 63A after passing through the upper case 67A and lower case 68A without passing through an infinite route. That is, the fact that the upper case 67A and lower case 68A serve as a part of the magnetic circuit represents returning the magnetic flux emitted from one side of the magnet 63A to the other side of the magnet 63A after making the magnetic flux pass through the upper case 67A and lower case 68A without making it pass through an infinite route.
Characteristics requested as performances of an isolator are a small forward transmission loss (insertion loss) and a large backward transmission loss (isolation). In FIG. 31, when assuming that the upper case 67A-side of the magnet 63A is N-pole and the lower case 68A-side of the magnet 68A is S-pole and most predetermined signals input to the input/output terminal 65Aa are output from the input/output terminal 65Ab, the direction from the input/output terminal 65Aa toward the input/output terminal 65Ab, that is, the transmission direction of the signals is the forward direction. That is, it is requested for an isolator that a signal output from the input/output terminal 65Aa toward the input/output terminal 65Ab has a small transmission loss and a signal output from the input/output terminal 65Ab toward the input/output terminal 65Aa has a large transmission loss. In practical use, the magnitude of insertion loss or isolation that can be assured in a desired frequency band is a problem. Because various improvements are attempted for an insertion loss and the peak value (minimum value) of the insertion loss is decreased, an insertion loss value that can be assured in a desired frequency band is also considerably lowered. However, because characteristics of an isolation are not adequate, the isolation of 15 dB or more recently required for the design of a portable telephone is not secured in a desired frequency band. That is, a band in which a desired isolation is secured is narrow before and after a desired frequency of a signal.
Moreover, the above conventional LUMPED ELEMENT TYPE isolator has the following problem.
That is, because the interval between the ferrite disk 62A and the case lower-side 68A is small, when the magnetic flux emitted from the permanent magnet 63A passes through the ferrite disk 62A through the case upper-side 67A and lower-side 68A of metallic magnetic materials, the magnetic flux density of the outer periphery of the ferrite disk 62A becomes higher than that of the central portion of the disk 62A and thereby, the magnetization distribution in the ferrite disk 62A is deteriorated.
The third aspect of the present invention is made to solve the problems of the above conventional isolator and its object is to provide a non-reciprocal circuit element having a superior transmission characteristic by improving the magnetization distribution in a ferrite disk and greatly reducing an insertion loss which-is an isolator characteristic.
To solve the above conventional problems, the first aspect of the present invention uses a non-reciprocal circuit element for transmitting a signal in one direction or cyclically transmitting a signal by using circuit means having at least a ferrite (34), transmission lines (31, 32, and 33), and a capacitor (21), comprising:
at least two external input/output terminals (11 and 12) for transferring a signal to and from an external unit and at least one of external grounding terminals (13, 14, and 15) to be grounded; wherein
at least one (13) of the external grounding terminals is set between at least one set of external input/output terminals (11 and 12).
To solve the above conventional problems, the second aspect of the present invention has an object of providing a LUMPED ELEMENT TYPE isolator having a large isolation band width.
To attain the above object, the second aspect of the present invention uses a LUMPED ELEMENT TYPE isolator comprising:
a ferrite plate having a predetermined shape;
three strip lines arranged on the ferrite plate and overlapped each other while electrically insulated from each other;
a resistance whose one side is connected to one of the three strip lines and whose other end is grounded;
a magnet set on the three strip lines so as to face the ferrite plate to apply a DC magnetic field to the ferrite plate;
a predetermined grounding electrode; and
a case for storing the ferrite plate, the three strip lines, the resistance, the magnet, and the grounding electrode to serve as a part of a magnetic circuit; wherein
the case has an opening in the length-axis direction of the strip lines to which the resistance is connected on the ferrite plate, and
at least a part of the case is electrically connected with the grounding electrode.
The third aspect of the present invention improves the magnetization distribution in a ferrite disk by setting a dielectric layer having a superior characteristic for a high frequency between a ferrite disk and a circular grounding plate and separating the lower case of a metallic magnetic material from the ferrite disk and reduces the insertion loss of an isolator.